The present invention generally relates to controlling the temperature of partial areas of a substantially flat object. More particularly, the present invention relates to a temperature-controlled chuck to hold a substantially flat object. With such a temperature-controlled chuck the temperature distribution of the substantially flat object can be sensed or measured, and due to temperature influencing elements the temperature of partial areas of said object""s back side can be altered to obtain a more uniform temperature distribution. Furthermore, the present invention relates also to a temperature-controlled wafer chuck and a method for controlling the temperature of a substantially flat object such as a wafer. Finally, the invention relates also to a pre-align station of an exposure tool for wafers comprising a temperature-controlled wafer chuck, and relates to an exposure wafer chuck in an exposure tool for wafers comprising a wafer chuck with which the temperature of a wafer can be measured and influenced as desired.
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer-shaped semi-conductor substrate, or xe2x80x9cwaferxe2x80x9d. The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide such as silicon dioxide is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist.
Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds such as diazonaphthaquinones, that under go a chemical change upon exposure to radiant energy, such as visible and ultraviolet light. The irradiated sensitizer material has different solution characteristics with respect to various solvents than the non-irradiated material allowing for selective removal of the photoresist. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers.
After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated through the use of a radiation opaque mask. The mask contains transparent portions that define the pattern for the next circuit layer. The mask is placed over the photoresist layer and the photoresist covered by the transparent portion is irradiated. The wafer is removed and the photoresist layer is exposed to a process liquid, known as developer. The developer selectively solubilizes and removes either the irradiated or the nonirradiated photoresist exposing portions of the underlying insulating layer.
The exposed portions of the insulating layer can be selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. In this process, the photoresist should be more resistant to the etchant than the insulating layer to limit the attack of the etchant to only the exposed portions of the insulating layer. Alternatively, the exposed underlying layer(s) can be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Thermal gradients in wafers during lithography exposure create linear pattern transfer effects due to expansion or contraction. Wafers can have temperature instability due to previous processing from a photoresist track hot plate. If this bake is non-uniform or the cooling prior to wafer transfer into the exposure tool is not complete, non-linear effects will occur. During the transfer from the track to the exposure tool there may not be adequate time for the wafer to thermally stabilize prior to exposure. This effect causes pattern transfer errors, seen as overlay or grid distortion and chip magnification errors. Other sources of non-linear errors can occur outside of lithography processing. These sources include rapid thermal processing such as anneal (RTA), film deposition processing (such as diffusion or chemical vapor deposition-CVD), and chemical mechanical polishing (CMP). These non-linear errors are variable across the wafer and are difficult to correct when severe.
A temperature difference as small as 0.1xc2x0 C. can affect overlay. Wafers can only equilibrate through conduction with the exposure tool environment or contact with non-temperature regulated surfaces, so-called chucks. There are defects during lithography processing known as xe2x80x9cbanana effectxe2x80x9d problems due to wafer contact non-uniformity on the track hotplate that cause significant temperature gradients over the wafer that result in overlay issues in these areas. Banana effect non-linear errors typically occur on the edge regions of the wafer in a semicircle pattern that resembles a banana shape. The magnitude of these non-linear errors varies significantly across the effected region, and therefore are difficult to correct using normal lithography processing.
Thus, it is apparent that a need exists for an improved chuck to hold a substantially flat object such as a wafer and a method for controlling the temperature of a wafer in a pre-align station or an exposure tool, which overcomes, among other things, the above-discussed problems to produce a more uniform temperature distribution over the surface of the wafer.
Furthermore, it is an object to provide an improved chuck with which the temperature of localized areas of a generally flat object, particularly a wafer, can be influenced in a desired manner to reduce significant temperature gradients over the wafer or to use defined temperature peaks or temperature depths in localized areas of a wafer to reduce or eliminate distortions of the wafer grid.
The above objects and others are accomplished by a temperature-controlled chuck and a method for controlling the temperature of a substantially flat object such as a semiconductor wafer, in accordance with the present invention. The temperature-controlled chuck according to the invention comprises a chuck body having an object support side and a back side, said object support side holding a substantially flat object having a front side and a back side on said back side of said object. A plurality of temperature sensing elements is distributed on said object support side to measure the temperature distribution of said object. A plurality of individual temperature influencing elements is distributed on said object support side to face said back side of said flat object, each of said temperature influencing elements being arranged to influence the temperature of a partial area of said object""s back side as desired.
A temperature-controlled chuck according to the invention provides the possibility to influence the temperature of a wafer, particularly the back side of a wafer, in a partial area in a manner as desired. For example, by use of an inventive temperature-controlled chuck the temperature can be varied precisely in tenths of a degree centigrade and be controlled overall to xc2x11xc2x0 C. Hence, a good temperature uniformity across the whole wafer would be provided. It is also possible to provide local modification to correct process distortions on a wafer. If, for example, the temperature in partial areas of the wafer can be precisely controlled, then it is also possible to use a variation of the chuck temperature to adjust for chip magnification error, instead of changing lens, housing pressure or having an extra field lens for magnification adjustment. It could also be used in conjunction with current lens magnification correction systems, so that a coarse chip mag correction would be done using temperature adjustment while the fine correction will be still done as of today. With such a preferred embodiment of the invention, a simpler lens design for an exposure tool is possible, and hence such an exposure tool can be constructed more cheaply.
A preferred embodiment of an inventive temperature-controlled chuck comprises a plurality of piezoelectric elements, each piezoelectric element being individually controllable, such that each piezoelectric element is able to influence a localized area or a partial area of the object""s back side. Due to a variation of the current and/or the voltage applied to the piezoelectric elements, the temperature of the object""s back side can be controlled in a desired manner.
A further embodiment of an inventive temperature-controlled chuck comprises the above-mentioned temperature influencing piezoelectric elements. At least some of these piezoelectric elements are arranged such that they are able to contact the back side of a flat object such as a wafer. Due to the contact of the piezoelectric elements with said back side of said flat object, influencing of the temperature of the back side of said flat object is improved.
In an alternate embodiment of the invention a plurality of support pin elements are distributed on said object support side and arranged to contact said back side of said flat object. In such an embodiment of the invention, the wafer is held on the support pin elements and piezoelectric elements also distributed between the support pin elements serve to measure or sense the temperature and serve to influence the temperature in a desired manner.
Another embodiment of the invention comprises individual fiber optics being illuminated with infrared radiation to influence the temperature of localized areas of the object""s back side.
If fiber optics as mentioned above are used to influence the temperature of localized areas of the object""s back side, in a referred embodiment of the invention the tops of these temperature influencing fiber optics are arranged such that they are spaced from the object""s back side.
A further preferred embodiment of the invention comprises a plurality of fiber optics illuminated with infrared radiation and a plurality of piezoelectric elements as temperature influencing elements. Due to the combination of fiber optics and piezoelectric elements a better temperature distribution of the object""s back side and a better influence of the temperature distribution can be achieved.
An alternative embodiment of the invention comprises also heat sink pins and heating elements as temperature influencing elements. Hence, in such an embodiment localized areas of the object""s back side can not only be heated but also be cooled.
Due to the use of temperature influencing elements which are selectively movable in close proximity with and away from said back side of said flat object, a better influence of the temperature of a localized area of the object""s back side is achievable.
Another embodiment of the invention comprises a temperature controller connected to that plurality of individual temperature influencing elements to control the temperature distribution of said flat object in a desired manner.
A preferred embodiment of the invention refers to a temperature-controlled wafer chuck comprising a chuck body having a wafer support side and a back side opposing said wafer support side, said wafer support side being adapted to hold a wafer having a front side and a back side on the object""s back side. A plurality of temperature sensing elements is distributed on said wafer support side, each of said temperature sensing elements being arranged to sense the temperature of a partial area of said wafer back side. A plurality of individual temperature influencing elements is distributed on said wafer support surface, each of said temperature influencing elements being arranged to influence the temperature of a partial area of said wafer back side. A temperature controller is connected to said plurality of temperature sensing elements and said plurality of individual temperature influencing elements to control and/or regulate the temperature distribution of said flat object in a desired manner.
A preferred embodiment of such a temperature-controlled wafer chuck comprises a temperature controller including at least one temperature detector and a control unit connected with said at least one temperature detector and controlling said temperature influencing elements.
A preferred inventive method for controlling the temperature of a substantially flat object having a front side and a back side and being supported on said back side comprises the method steps of sensing the temperature of partial areas of the back side of said flat object, determining the object""s temperature distribution on the basis of the temperatures measured in said temperature sensing step, and changing the temperature in at least some of said partial areas of said back side of said flat object in a desired manner.
The method is particularly for controlling the temperature of a wafer held on a wafer chuck.
In a preferred method according to the invention, the temperature of a partial area of said flat object is measured by a temperature sensing element of a plurality of temperature sensing elements distributed over the back side of said flat object.
In a preferred embodiment these temperature sensing elements consist of a piezoelectric element.
In a preferred method according to the invention the temperature of a partial area of said flat object is influenced by a temperature influencing element of a plurality of temperature influencing elements distributed over the back side of said flat object.
In a preferred embodiment each temperature influencing element is an IR-optical fiber.
In another preferred embodiment of the inventive method each temperature influencing element is a heat sink pin.
In an alternative embodiment of the inventive method a piezoelectric element is used as a temperature influencing element.
Another embodiment of the inventive method includes IR-optical fibers and piezoelectric elements and heat sink pins as temperature influencing elements.
A preferred embodiment of a pre-align station of an exposure tool for wafers comprises:
chuck body having a wafer support side and a back side opposing said wafer support side, said wafer support side being adapted to hold a wafer having a front side and a back side on the object""s back side. A plurality of temperature sensing elements is distributed on said wafer support side, each of said temperature sensing elements being arranged to sense the temperature of a partial area of said wafer back side. A plurality of individual temperature influencing elements is distributed on said wafer support surface, each of said temperature influencing elements being arranged to influence the temperature of a partial area of said wafer back side. A temperature controller is connected to said plurality of temperature sensing elements and said plurality of individual temperature influencing elements to control the temperature distribution of said flat object as desired.
A preferred embodiment of an exposure chuck in an exposure tool for wafers comprises
a chuck body having a wafer support side and a back side opposing said wafer support side, said wafer support side being adapted to hold a wafer having a front side and a back side on the object""s back side. A plurality of temperature sensing elements is distributed on said wafer support side, each of said temperature sensing elements being arranged to sense the temperature of a partial area of said wafer back side. A plurality of individual temperature influencing elements is distributed on said wafer support surface, each of said temperature influencing elements being arranged to influence the temperature of a partial area of said wafer back side. A temperature controller is connected to said plurality of temperature sensing elements and said plurality of individual temperature influencing elements to control the temperature distribution of said flat object as desired.